This invention relates to pressure release devices for internally pressurized fluid containers.
Pressurized fluid containers are in widespread use for packaging and dispensing a variety of fluid products, including liquids, gases and combinations thereof. Under normal operating conditions, such containers perform entirely satisfactorily. However, in the event that the contents of such containers should become over pressurized, either because of improper use, exposure to heat or for any other reason, then a violent rupture may occur. For the last 25 years, those skilled in the art have been attempting to solve this problem by incorporating various types of pressure release devices into the container structures. Examples of some of these previously developed pressure release devices are disclosed in U.S. Pat. Nos. 2,795,350 (Lapin); 3,074,602 (Shillady et al); 3,292,826 (Ablanalp); 3,622,051 (Benson); 3,724,727 (Zundel); 3,815,534 (Kneusel); 3,826,412 (Kneusel); 3,831,822 (Zundel); and 4,003,505 (Hardt).
In each of these prior art arrangements, either the container bottoms or the container side walls are scored or "coined" to provide weakened areas. These weakened areas are designed to separate and release the container contents under controlled conditions and at selected pressures beneath those at which more violent and potentially dangerous ruptures are likely to occur.
A major difficulty with these prior art arrangements, however, lies in the fact that in order to weaken a side or bottom wall sufficiently to achieve a selected release pressure, the coining often must be relatively deep. For example, assume that a pressure container has a circular internally concave bottom 2.545" in diameter fabricated from 0.015" deep drawn tempered steel, and that the bottom is coined to provide an integral generally circular pressure release tab with a diameter of approximately 0.427". In order for the tab to release at a selected pressure which is above 270 psi (minimum release pressure established by the U.S. Department of Transportation) and below a pressure at which a container wall may experience an uncontrolled violent rupture, the coining operation must be carried out to a depth of approximately 0.014", leaving an intact web underlying the coined indentation of only about 0.001". Because of the embrittlement produced by work hardening during the coining operation, such relatively thin webs are highly susceptible to damage and premature rupture during subsequent normal handling and use of the containers. Moreover, these relatively thin webs often develop microscopic cracks or fissures which allow the container contents to leak.